Hydraulic power system



3 Sheets-Sheet l E. J. POITRAS ET AL.

HYDRAULIC POWER SYSTEM Filed June 6, 1935 INVENTORS Edward Poitras Jannes D. Team BY THEIR ATroREY API-i129, 1947.

April 29, 1947.

E. J. POITRAS ETAL 2,419,792

HYDRAULIC POWER SYSTEM "N Filed June e, 1955 5 sheets-sheet 2 `THElR ATTORNEY 5 Sheets-Sheet 3 E. .1. PolTlAs ET AL HYDRAULIC POWER SYSTEM Filed June e, 1955 XXXX XX X

X X X X X X THEIR ATTORNEY April 29, 194'?.

MNQW

Patented Apr. 29, 1947 HYDRAULIC POWER SYSTEM Edward J. D. Tear,

Instrument Company, N. Y., a corporation of Poitras, Jackson Heights, and James Great Neck, N..Y., assignors to Ford Inc., Long Island City, New York Application June 6, 1935, Serial No. 25,208

l 'I'he invention herein disclosed relates to vhydraulically operated systems and in particular to controls for regulating theow of the hydraulic medium and the operation of hydraulically operated devices.

4Although the invention is not limited to any particular application, it has, in some respects, especial utility in a hydraulic System utilizing a hydraulic motor. Heretofore, it has been the common practice to control a hydraulic motor by regulating a valve through which the liquid owed to the motor. However, the rate of .flow of liquid through an orice, such for example, as a valve, is dependent upon the pressure drop across the valve as Well as the valve opening. A valve alone does not, therefore, provide a satisfactory device for regulating the speed of a hydraulic motor as the pressure drop across the valve will vary with variations in the reaction torque on the motor, and the speed of a hydraulic motor of the positive displacement 'type is dependent upon the rate of flow of uid through the motor. Y

By this invention, control of the rate of ilow of a hydraulic medium and the speed of a hyydraulic motor of the positive displacement type is effected by controlling both the area of an orifice through which the liquid passes and the pressure drop across the orifice. By maintaining one of these factors, upon which the rate of flow of liquid depends, constant, the speed of thevmotor may be controlled by a single operating element affecting the other factor. It isV noty material which of the two factors is maintained constant although it has been found preferable to provide a valve, for varying the area of an oriiice through which the liquid flows, and to maintain the pressure drop across the valve constant. With such an arrangement, the speed of a hydraulic motor of the positive displacement type may be regulated by movement of a single control element. Y Y' l In accordance with the invention, thepressure drop across the valve is maintained constant by varying the pressure of the supply. The pressure drop across the Valve is in this way maintained constant irrespective of the load on the motor and the speed of the motor is, therefore, independent of the load and varies proportionally to the opening of the valve. Such a system is illustrated in the accompanying drawings in which: l Fig. l is a diagrammatic illustration ofthe complete system;

22 claims. (ci. (s0-5s) Fig. 2 is asectional elevation, partly-diagrammatic, of the controller; Y v Fig. 3 illustrates a modified for a modified systemyand ...f

Fig. 4, illustrates another formcf regulating valve.,

regulating valve Essentially; the system includes liqudunder pressure which is representeduby a pump l, a controller 2 andahydraulic motor 13, the controller being interposed Ybetween the pumpl and the hydraulic motor 3. In the-sys,- tem illustrated, the pump l is of the constant displacement type which supplies a constantfvol.- urne of liquid per unit of time and` it is directly connected to an electric motori! b y-meansof which it is driven at aV constant speed. The pump supplies a hydraulic medium, preferably-goiLfor the operation of the hydraulic motora Sincegthe system illustrated is one forrcontrollng'the velocity, both speed anddirection, of the vhydraulic motor, both v the intake and output sidesoffuthe pump are connected -respectively loy conduits 5 and B .to the controller. Likewise, both passages to the hydraulic'motor are connected by conduits 1 and 8 to the controller. 1;;9

The controller 2 is a valve block forming a housing for, and including interconnecting ports and passages between an overflowforreliefivalve 8, a reducing valve l0, a pressure regulating valve il, a four-way control valve l2, a hydraulic amplier actuated by a pilot valve ,I3 through which the four-way valve l2` is operatedand an advancing or synchronous valve I4. AThe overowrvalve 9 is utilized as -a safety valvefor the purpose of relieving exessive pressures which may develop under .certain conditions of operation. In the systemillustrated the pump l is capable of supplyingr oill at a pressure of approximately`V 1000 pounds perv square inch, hereinafter` called4 the high pressure, and in the event that the pressure in the supply line materially exceeds this llvalue, the relief valve connects the supply line to the exhaust. lThe reducing valveprovi'des a supply of loil at lowf pressure, approximately pounds per square inch, which oil is used in the actuation of the pressure regulatingvalve VI-IV andlthe amplier for operating the four-Way controlfvalve.

The pressureregulating valve maintains the drop in `pressure across the oil supply opening, through the four-Way valve to the motor, constant at approximately 100 pounds per square inch. This pressure Adrop is maintained, across the' supply passage through the valve irrespective of lwhich one of the two motor leads is Vconnectedto'the supply by the four-way valve which controls the T oFFlcE- direction of the flow of the fluid delivered to the motor as well as the rate of flow of the liquidi. The four-Way valve is of the piston type and is provided with ports and passages so arranged that either motor lead may be connected to the high pressure and the direction as well as the speed of the hydraulic ntorthis contjlled; fmfj' way valve is hydraulics; ly opratel'thrugh an arrangement which is plifler. The operation of the four-way valve lis controlled by the pilot valve I3 which responds to a very slight force.

The overflow valve 9 well known type in which Ytllfofr'c-'fthe pressure of the oil supply is exertdgaihstfcalif brated spring. The valve consists of an elorrgatedl cup-shaped member which is receivedina here 2a in the valve block 2 which bore forms a valve termed a hydraulic am- 'T0 #adjacent the block I1, the upper end of the valve A as seen in Fig. 2, is hollow and communicates Y with't'h chamber formed by the andrea chamber. Surrounding the bore and sp'ac'dln`L` f' gitudinally thereof, there are two circumferential ports aland fsb. Thesefpoitsfddmmunicte A.v-1th pipe taps 2b and 2c to hltfhthhlcnduitsr and 5 are respectively eni'ie'cted. Avplate leiesesthe end of the bore in whiehithevalvefis ifs-'mounted nr'idlp'revids an atutmnt'agaiust tvriiehenee'nd cf a calibrated spring IB labuts. The other'ind To! tne'caiibratedispring Ait abuts f'lgainst theiriner edfoffthe'fcup-shaded valvejsfand sets to' move tire `valve longitudinally or. fthe bore. away frfrom the prateria The'vaive e. includes we sets of epemnsfs andyd, throughthe cylindrical .part thereof The several v'c'iir'civiinferenti'ally spaced p'e'nlngs' 9c "eeoperatewith the pbrt sa. The sev: `eral ircuiirentiallgf spaced openings 's'd 'are lspaicedlffpmthe epeningsfe longitudinal-1y of the fval've' and cooperate "'iththeport ab. 'A'pert fse p'mnuni'cates witnfthe'fspac'e l between theinn'er Feiidfnfftiie .valves-and jen' end of a bleek 'lil secured in and idlividing'the here zewhichj extends ftiirougnftnevalve .biefeka 'rh'epertfse also coinmnicatswithlthe high pressure-permet se that itheifreeexeit-edflby the'high'piessure eilag'ain'st Afrirefend estrie-valve is exerted against the farce 'exerted by tnespring fi sf. i lIfjthe.pressure in the port 9a increases beyond@ derta'inprede'termined valine;the valve:Ili'sV 4vovedagaiiist'tliie'Iactin of rirefspnffig'upward IaSseen in Fig-ure 2, and. me fepemngsse-'ceff an are denture srtfsa. refs'ulesientninwslfrem tnelpr'e sei-irte the @tener/lef 'ehe valve @s and 'aliene-ene verve, ltrfr'dgrfenefdpemngssalenntefure exriaestgpen sb,- ene recense trie .pressure the part @pressure rn triefpdrtieafereps 'te 4the pedet'rifiined velue," use valve ls v ehe -bp'site'aieeun te iure-'fiese infinfwruenfajis Tarieven mitigare- 2 m'wjhie'eais the penna is liasses. grae `feree exerted-py the 'en 'the thi's Eacts'"against"tif-ie*spring Eiland nieves e viv'e' te Arelieve 'rdesspressufes 'indie time; n,

The hdreazeaiso feriasT vaiveenarn'eer ferme rcirfe-reiifeliimening-iemand'von eine apposite sfide errrrejbieek 1ro that on 'me Jvalve e repeated. aine 'ein verven se fgedfuier there is epe-ian frreesf-'xfereedsy the en pressure ande celebrates spring epes'tehenigrfwessdrelwnen 'the `lcv! npressure fprt'islss than ade; ei'e's'es' 'when 'die pressnref-rnfuie aieerseinv fill' 4 sure and exhaust ports. A circumferential high pressure port Illd is formed in the block 2 at a position to cooperate with the enlarged section IIIc of the reducing valve. A similar circumferential exhaust port I0e is also provided and located so as to cooperate with the enlarged section 10b 'f thevlve. v.il ylow prislie'pt gIllffcmmunihates withlthe valve c amber between Ythe high pressure and exhaust ports. The end of the valve reduced portion f'ef ,the valve through a diametral passage Ing has access to y The pressure of the oil 'acting between the end surface of the block II` and the surfaces formed on the interior of the valve tend to move the valve away from the block I1,4 downwardly as illustrated in Fig. 2, and, thus, close the high pressure port and open the exhaust p'ort. rvrTheAfo'rceexerted by this 'ciluh'der pessureis resisted by a spring iwhich 'acts betwena plate IB, securedlbver the opening to the -box'eaI and the" end soi` the valve. An' abutment pin 20 extending from the plate ISand intoth'e vvalve limits the 4exte'ntut'he valve maymve in theidirection of'theplate I9. TIt'will be seen-that wlenthe pressurein the low pressure port'exce'eds a value represented by the calibrated-'spring xIIL'the valvefismoved'so'aasfto cut off the high .'pres'sure lpo'rt and "open'i'the low pressure .portto exhaust. '1f ori'th'e otherhand the 'oil in the` lo'w .pressure port is below the value represented by thesp-ring t8 the valve is 'moved in the opposite direction, upwardly as rseen in-Figure `2, so that theexhaust port -isf'losed andthehigh pressure port is, placed into communicatin with the low pressure port. The valve. thus maintains a supply oflowipres'sure oil at 'a constant pressurey o! 'ap-- ,proximately r100 pounds Vper squareinch.

Jhe pressure regulating valve II vis `also 'operfated by: opposingffrcestheforce'exerted by the oil in the high pressure passage acting toim'ove the 'valvefin one direction .and-,the sum of a vconstant force, and'thezpre'ssure exerted bythepressure .0f ',eil'fin onexior the rother othe motorleads or passages, thefoil of higher .pressure being se'- -lected. acting'to move the valve in the opposite :direc-tion.. The valve II isof thebalanced piston valve type'havin'g aireduced central portion I Ia'. -It4 isfslida'bly'mountedn "a bereid, ada'cent 'one end v of they-bore, Iwhich extends transversely of the.. blocke'an'd parallel to.` thezb'ore l221. One end cf'thezbore 2d, the lower :end yas seeni-nFigure -2, isclosedby-aplate-Z" andl -thefother end -is closed ,'by aipla'te-2 I1. Intermediate the'ends of 'thebore .fthere is a stationary block y-2.". forming a partition between/the valve` Ifl f vand the operating mechamism-therefor. ,1n-theuportion `of rthe bore -2d jfprmingffthe chamber or the valve I I., `there is for-med a circumferential exhaustport I Ia-which `'71 The oil in the chamber is`4 in communication with the exhaustportfb. spaced longitudinally of the valve from the exlfst port II a,` there is a circumferential pres- 'Iewer end er 'the' valve-11, there rs prevrde'd e 'passa aannam hamberllfla-fermedlbetweenjthe end formed bythe reduced portion er the vewelilfena srejiia "I lbfwhienjjis connected te me high presser'eiper;v sa" ef 'the 'valve s. 'rnreugnme i lerell-ef wnienpieces the chamber formed-bv llrhef reduced' portion "of the `valve in communicalif 'fenelvervesnd the plate zo". 'n 'wu be observed tha-tithe port Hbcmmunica'tes with the lchamber tltfroughtl'le passages-Hc with "the Achamber II-Id.

valve away from the plate 20' and place the ports IIb yand I Ia into communication so that` oil flowing through the port IIb will pass to the exhaust IIa, thus reducing the pressure of the oil in the port IIb and the passages communicating therewith.

.This tendency of the valve Ii to. move in the direction of the block 22 is resisted by the low pressure oil in a chamber IIe between the block 22 and the end of the valve II. The chamber IIe is connected to the lowv pressure port luf of the valve. lil through a port IIf. In addition to the force exerted by the low pressure oil on the valve Ii, the pressure exerted by the oil in the chamber Hd is resisted by the force of the oil in one or the other of ports I Ig or Ilh which communicate with the bore 2d on the side of the block 22 opposite to that on which the valve I I is located. Within the upper section of the bore 2d there are tted two pistons or plungers 23 and 2t. Each of theseV pistons is of cup-shape, the closed ends thereof facing each other. On the adjacent ends of the pistons 23 and Zfi there are formed lugs 23a, and 2da which abut against each other when there is no pressure in the port IIlt or the pressure of oil in the port Iih is less than the pressure in the port iig. The port Hh normally communicates with the bore 2d between the plungers 23 and 24. The port Iig communicates with the bore 2d on the opposite side of the plunger 23 to that side on which the port i Ih communicates. The plate 2i carries an abutment pin 25 which limits the movement of the plunger 23 in a direction away from the plunger 2li. The block 22 has a reduced extension 22a which extends into the hollow piston Z and forms a limiting abutment for this piston. Extending through an axial bore in the block 22, there is a rod Z which abuts at one end against the piston 24 and at the other end against the end of the valve Ii. The chamber formed between the piston 24 and the block 22 is placed into communication with the exhaust so that any leakage passes to the exhaust. The exhaust communicates with this chamber through a port lli.

With the arrangement illustrated it will be observed that if the pressure in the port Ilh is greater than the pressure in the port iig, the plunger 23 will be forced against the end of the abutment pin 25 and a force will be exerted on the plunger 24 which is equal to the area of the surface of the plunger 24 times the pressure in pounds per square inch. This force will be exertedthrough the rod 2S on to the valve I I. On the other hand if the pressure in the port IIg is greater than the pressure in the port Ilh, the oil entering the port Iig will cause the plunger 23 to abut against the plunger 24 and the force exerted by the oil passing throughv the port IIg will be transmitted through the plunger 24 and the pin 25 to the valve Il. With this condition existing, the oil passing through the port I Ih will have no effect as it will be balanced between the plungers. It will thus be observed that in addition to the pressure exerted by the low pressure oil in the chamber IIe, there will beexerted on the valve I I a force which is created by the pressure oi` oil in the port I Ig or I Ih., depending upon which of the two is of the higher pressure. In other words, the plunger arrangement together with the rod 26 forms a means by which the greater of the two pressures may be selected and added to a constant pressure to resist the movement Vofthe valve under the action of the oil pressure in the chamber Hd. Itis alsor to be noted that the oil pressure in the port I Ib will` be equal to the pressure in either of the ports IIg or IIL, depending upon whichv has the oil of higher pressure, plus the force exerted by the low pressure oil which is approximately pounds per square inch. There is thus always maintained a constant drop in pressure of 100 pounds per square inch between the oil in the port IIb and the passage connected thereto and either of the ports IIg or VI Ih and the passage connected thereto The port IIb of the pressure regulating Valve is connected to a high pressure port in the fourway control valve which controls communication between this high pressure oil passage and the motor. The four-way valve I2 is an elongated cup-shaped element of circular cross section. It is slidably mounted in a cylindrical sleeve 21. The cylindrical sleeve 21 is slidably mounted in a bore 2e extending transversely of ,the control block and parallel to the bores 2a and 2d.. Ports 21a, 2lb, 21o, 27d, 27e and 2If are formed in the wall of the bore 2e. Each of these ports is a circumferential port formed by recessing thewall of the bore 2c. The ports 27a, 2lb, 21o, 21d, 21e and 2'If cooperate respectively with openings 21a', 2lb', 21e', 27d', 21e and 21]" through the valve sleeve 21. The valve sleeve 2l has a circumferential recess formed in its outer wall for each of these series of openings through the valve sleeve. For the openings 21a. to 21e', thereare also formed circumferential recesses in the innerY surface of the valve sleeve 21.' The ports 21a and 21e are exhaust ports and the inner circum-v ferential recesses are provided so that a Very minute opening of these ports is equivalent to a full opening of the ports 21d and 2lb which are motor ports. An end plate 28 closes one end, the lower end as seen in Figure 2, of the valve sleeve 2 and there is formed between the end plate 28 and the adjacent end of the valve I2 a chamber 29. A plate 3E closes the lower end of the bore 2e and a cap 3| on the upperv end of the valve block closes the upper end of the bore 2e. The cap 3i has a central axial extension 3Ia which extends into the valve I2 and a chamber 32 is formed in part in the cap and in part in the bore 2e into which chamber the end of the valve I2 and the end of the sleeve 21 extend. As indicated by the diierent types of lines, the ports 21a and 27e are connected to the exhaust. The ports 2lb and 21d are connected to the ports IIg and IIh. respectively and also the tapped passages 2f and 2g which are respectively connected to the motor leads 'I and 8. The port 21e is connected to the high pressure, that is, the port IIb of the pressure regulating valve, The

arrangement of passages and the interconnec` tion of the ports is indicated by the diierent lines and the nature of the passages represented by these different lines is indicated in the legend on the sheet ofv drawings containing Figure 2. In this legend the following abbreviations are used:

HP for High Pressure. EXI-I for Exhaust.

LP for Low Pressure. M for Motor Passage.

ning the various ports and openings through the sleeve 27. It will be observedpfrom Figure 2, that` animee when the valve I2 is moved .up .relative :to 'the sleeyefsl, the :port Lzd isplaedfinto communication `with the exhaust ,port 21e .through Ythe passage .formed by =the groove I2`cZ-.ain '.thevalve. Also the port. 2'Ic;is .placed into :communication with the :port 21h. Thus, the high pressure nii flowsfromthe portlc to the port `2:1 b'andLfrom placed into communication with thefexhaustzport 21a. Under these conditonsytheoil is vdelivered through the motor in a. directionoppositelto that in 4which it was delivered when the valve was movedin the other direction and the pressureofVv theioilfn the port .Iih `predominates.over that in the port Iig, and the'regulating valve II'IIis actuated in accordance with the pressurer in the port Hh.

The hydraulic Aannoliiier is used-so that relative movement between the sleeve 2,1 and the valve .I2 may beeiectedbya minimum of eiort. Relative movement of the sleeve .'21 Vand 4the valve l2 .is eiected by controlling the -owof low-pressure `oilito and from-the chamber 29. This control isieiected through the pilotv valve- I3` which is` operated through. a valvey rod 13a that extends through the center ofthe valve lf2 andthe-extension 3Iaoflthe capii/I. The valve I3 is a balancedpiston valve having a. central :reduced lportion I3b 4and1it is mounted .in a .Valve chamber I-Zf'formed inthevalve I2. A passage I2g, extending transversely' of` the valve 'I2, connects the valve port I2e and the valvecharnber 'IZ at the reduced portion-of'thevalve I3. Intheznormal position, as seen in Fgur'eJZ, `the valve |13. lapsthe end of a passage I2h which connects the valve chamber I2f to the chamber 2.9. An exhaust passage I2i runs parallel .tothevalvef chamber .I2f andconnects the end of .that chamber with '.the "hollow section of the valve I2. It will beseenvthat when the valve .I 3.ismoved .upwardly as seen in Figure 2, thereduced central :portion willispan the passages 12g-,and I-Zh and. oil at 4the low. pressure will 'enter through the .porti 2-'If through .the passages 12g 'and I-2h and into the chamber 29 wherein it will. exert aiorce .tending to movethe -valve I2 within the :sleeve 21 inthe same .direction as the valve TI 3, that is, '.upwardly.

The lowxpressure :is .also connected. to the cham` berr32 andacts on Vthe endof the valve I2'which extends :into .this chamber. The area of the lowe1` :face of ithe valve :I2fismuch greater thanI the areaof the end'of the 'valve projecting into the chamber 32. Therefore, whenithe lownpressure voilis admittedto chamber '29, the valve'is moved against the oil pressure in chamber 32.

However, when the chamberlZ'Sl-' is connected to the exhaust, the oil pressuref-inlchamber -32 forces the valve down. Therefore;whenthevalve I3 is moved downwardly in `:the valvechairiber` I2, and the passage I2h is placed into communication with the hollowsecti'on 'of-'the valve "I2fso that-the oil inthe chamber'imaybeexhausted,

the small quantityof oil #treme-that chamber' trickling l'out 4through the passageL 5tlfrrougfn th'e f extension v3l through which the 'valve -rod"I3a extends, fthe-:pressure of the :oil in :the fchamiier 32fcauses rthe valve :lf2 nto .fmove downwardly.

zuheaoperation'oi Xthezsystcm Iin so dan'. aasittlhax been-xie'scrible'dis :aszfollows: In :the tpoaitionfn! the martstofithefcontrollerfillustratedinlgure 4, the ports 2lb and 21d are lapped by the valveiIlf, themotorris-cut off :from the supply foil an'dit isat rest. If' itbe desired toeffectth'eoperation of the fmotor, the'valve rod I3a is rn'ioved',..up=rn down depen'ding upon ythe direction whichzzit is desired to have the motor operate. ,Let :usf 9sslmietha't'the valve rod I3ais moved` upwardly so`that the reduced section I3b-df'thefvalve'spans the passages I2g and I2h. Low pressure ol'is then admitted through the passage EIIZ'g andthe passage I2h to the chamber 29. The'fpressure on the vioilin the .chamber 29fcau'sesfthe valve'i to move upwardly. AWhen :this relatlvetmovement occurs, .thereducedfsectionl2cfof the' valve I2 spans the high pressure port and-.the :motor port '2lb which are placed i'n communication. @il under the highpre'ssureisthus admittedt .the .port 21h and through the itapped'passage '2 and the conduit 1 .to the motor. The high ipressure oil port is also placed Ain communication with the port IIy and .the chamber behind the plunger '23; The pressure of Ythis oil iSfItherefore, added to the pressure of vthe'low pressure oil Ato move 'the valve 'I.I against the foil pressure in the chamber I Id thus regulating the' lpressure in the .port IIb and the high pressure port 21o of the four-waylcontrol valve in accordance-with the pressure 'of the oilactng. on the 'motori Ii the -load on themotor .is heavy, the '.fpiessurein the port 2lb and motor passage rwill build up, butlat all times the .pressure in `the .port lcxwill bey .pounds per' square J.inch higher .than the pressure inthe ,passageilb dueto 'the laddi'- tion of lthelow'pressure of 100 pounds per vsquare inch acting upon the valve 1| l in conjunctionfwith thelpressure inthe chamber behind thezpiston .28. There WiILtherefore, be afdrop'in pressure across therva'lve of." 100 lpounds per square inch .and the rate ofi flow vof y oil through thev valve fand .to the motor will be proportional toxth'e port opening.

If it be assumed that the valve rod I3a was movedfa certaindeniteiamount, it will be'seen that fthev'alve I2 will :follow '.the movement 'of the valve I3until the passage I2hfis closed. 'The valve @I2A moves the :same amount as thevalv'e` I`3f and Athe port opening is .'-proportional .tov the movement of the valve rod I3a'. Under 'these circumstances, the rateofow or oil I'to 'the inntor will` be constant and proportional to the movement othe valve'v rod I3a. Therefore, the

speed 'oftheimotor'willalso,beproportionalto the movement ofthe .valverod 13a.

Let Tus :now assume .that the motor :is E1n :operation due to :the movement iof the valveasdscribed' above.: fIffthe .motor is'eoperatihgwat :a constantlspeeddue to the valve fI3 being heldxa denite tamount lout of 'itsneutral zor .oi posi'- tion Awth'respect. tothe `valve block 2; the vrelation of :the valveil #and fthe fvalve I.2"will vliefthe' same'1as:illustratedlin`FigurezZ. 'lf the .valve rI3 is 'now returned to :its voriginal fposition, it :first moves .relative tothe .valve :I 2, and,-consequently, places theipassage 12h in 'communication with the interio'rof -the lvalve' I2'andthi1s'tofthe1atniosphere'. Thecpre'ssure 'in 2the chamber ,-29 'is reduced.andthelpressure on'the upper 1 endfof'the valve 1I2 due y-toi'the oil 'under pressure in Ithe chamberf32 fcause's Vthe 'valve' 'I2/to :move 'downe neutral position with respect to the control block, as shown in Figure '2,'th'e partswill assumethe positions vasthey are shown in' Figure 2 and the motor will be cut off. If, however, the valve I3 is moved downwardly'b'eyond its neutral position With respect to the valve block, the valve I 2,V following the valve I3 Vunder the circumstances J'ustmentioned will cause the reduced section I2c of the valve I2 to span the ports 21e and 21d. Thus, the oilunder high pressure will be admitted to the motor passage 2g and conduit 3 'and also to the port Hh andthe chamber between the plungers 23 and 24, the port Ilh being connected to the port 21d as previously described. Like- Wise, the port 2112 will be placed in communication with the exhaust port 21a since the section I 2b of the valve will span these ports. Thus, the side of the motor represented by the motor lead 2g will be connected to the high pressure and the motor lead represented by the tapped passage 2f will be connected to the exhaust, and the motor will operate in the opposite direction; and, as explained above, the speed of the motor will be proportional to the movement of the valve I3. It will be noted that the pressure regulating valve will now be actuated in accordance with the pressure in the chamber between the plungers 23 and 2Q so that the pressure drop across the valve will be again 100 pounds per square inch.

If it is desired to operate the motor in synchronism with another movable object, as in the system illustrated in Figure l, wherein the motor is operated in synchronism with a Selsyn receiver 34, the valve rod i3d is actuated in accordance with the diiierence in movement between the Selsyn receiver, and the hydraulic motor 3. The Selsyn receiver of course follows the movements of a transmitter which may be located at any remote point. The Selsyn receiver is connected to a differential 35 similar in all respects to the differential illustrated in our copending application Serial No. 15,758, filed April 11, 1935. The Selsyn motor operates one side of this diierential. The other side is operated through a gear 36 which meshes with a gear 31 secured on a shaft 38. Another gear 39 also mounted on the shaft 38 for rotation therewith meshes with a pinion 4I) mounted upon the shaft 3a of the hydraulic motor from which shaft an object may be driven. The dierential 35 is such that the diierence in movement between the receiver motor and the hydraulic motor is reproduced as longitudinal movement of the valve rod i3d. 'I'he gear train described and connecting the differential to the hydraulic motor may be such that an object driven by the hydraulic motor operates in a one to one ratio with respect to the transmitter which is connected to the receiver 34.

In the above method of operation, with the system so far described, the lhydraulic motor must necessarily lag behind the Selsyn receiver since the operation of thevalve rod I3a is dependent upon a diierence in position or movement of these elements. To eliminate this positional difference and secure a synchronous relation there is provided the advancing or synchronous valve I5. This advancing or synchronous valve is a needie valve raving along stern Ma. The stem Ilia is'made long in order that the expansion andA contraction will compensate for changes in the temperature of the oil; The valve stem I4a has formed on the end thereof a threaded section I4b which isreceived lirl' a" threaded recess in the valveV block. By means o1.'- this threaded end section I'4b, 'the needle valveM may beadjusted with respect to its valve seat. 'Ihe stem I4a extendsalong a passage vor bore 2h.' in the control block. The passageh connects the valve I4 anda passage I4c which ex-l tends between the passage 2h and an annular chamber 3Ib formed 'by reducing the diameter of the cap extension 3Ia. The valve I4 controls the rate of ilow of oil between the bore Zh'and the chamber 33. The direction of the flow of oil through the valve I4 is controlled by the valve I2 which is provided with a slot I2 adjacent its upper end and positioned to cooperate with the chamber 3Ib and the chamber 432, and a slot |27' positioned to cooperate withthe chamber 3| b and the exhaust port 21a. In the position shown, it will be observed that the valve I2 laps the chamber .3l b. However, if the valve I2 is moved downwardly, the chamber 3Ib is placed into communication through the slot I2' in the valve with the cham-ber 32 and oil at a low pressure flows from the lchamber 32 to the chamber 3Ib, and through the passages I 4c'and 2h, the valve I4 and passage ld to the chamber 33. This oil causes the valve sleeveV 21 to move upwardly, that is, in a direction opposite to the direction of movementof the valve I2. On the other hand, if the valve I2 is moved upwardly, the chamber 3Ib and consequently the chamber 33 through the valve I4 is-placed into communication through the `slot I 2j with the exhaust port so that oil Vis exhausted from the chamber 33 and the pressure on the upper end of the valve which extends into thelchamber 32 causes the valve sleeve 21 to move downwardly, again opposite to the valve I2.

It will be observed that this actonof the sleeve 21 due to these portsv and passages is 'additive with respect to the movement of the valve I2. The ultimate eiect is that'the motor ports .are gradually opened a greater amount than they would otherwise be by the diierence in movement between the Selsyn receiver'andthe hydraulic motor. Consequently, the motor speed lis increased and the object driven thereby isbrought into synchronism with the movable object which is operating the Selsyn receiver. Likewise, when the Selsyn receiver comes to rest this additive factor brings the object driven by the hydraulic motor into positional agreement With the object eiecting the operation of theSelsynreceiver.

The arrangement ofthe valve yI2-vvithin`tlf1e sleeve 21 is'A for the purpose of obtaining a large movementwithin a' limited space, There are provided, however, certain arrangements ,for limiting the relative movement between the sleeve 21 and the valve I2 to one 'unitpofv movementV in either direction from the relation illustrated in Figure 2. For this purpose, there is provided a passage Y21g. When'the valve I2A moves Ydownwardly Withfrespect to the valve' sleeve 2'1 one unit of movement, one end ofthe passage 21g is placed into communication with the exhaust'port 21e;'the other end of the passage is in communication with the chamber 33 and pressure in the chamber 33 is thus relieved. When the valve I2 moves upwardly', one unit of movement Awith respect to the sleeve 21, the passage 21g is placed into comlmunication with the low pressure port 21f. Thus, after one unit of relativemovement the valve I2 'and the sleeve `21 Vmove together. To ensure this condition mechanical means are'also 'proyvided for capturing the valve I2. For example, if

the valve I2 moves upwardly with respect vt'cfthe valve xsleeved# 4onen-unit. ofmovement; .the 'shoule der. formed' by( -theiA reduced; portion. 12u; of; the valve .l2 will abut. againstansannulan endl piece l-llsecured to the uppenzendr of.. thevalveV sleeve 2,1. If .onr the other hand-fthe: valve |122 moves downwardly' with; respect torfthe valve sleeves 11 one. unit of movement `a; lug '421. formed. on` the epd offthe. valvel 2; will abut .against lthe plate: 2li; Inxthe controller. illustrated in FigurevZ, control of". therate. of flowl ofliquid through the motor is. effectedV byl maintainingr a constant. drop: in pressure e across avalve through whichthe high pressure. side Aof the motor communicates: with the 74supply; of liquid-- under. pressure. However; the, samegcontrol-` may be effected by; maintain ing... a,-constant. drop in pressure. across a. valve through which the lowv pressure-side of: the. motor communicates with-anexhaust passager. .In this' latter Aarrangement,.the pressure inA` theexhaust passage isA constant:l and the back pressure on the motor-A may be,- ,maintained constant; .by regulating .the pressure of thesupply in; accordance .with the back pressure on the:l motor. If the backA pressure on the motor'is maintained: constant in` this way; andasstatedthe-pressure in the 4exhaust passage-isconstant,A the dropzir'rpresisure.v across a. valve` controlling; communication between the lowpressure sidei of; the2-motor and thetexhaust will-be constant.. The rateof. flow oil liquid from.y the motor,4 and consequently; the rate` ci. flow of: liquidy through vtheA motor' will', therefore, .be proportional to'thea valveropening.. Y Ir'iicertain installations, it4 is. preferable to: con.- trolv the. motor: byY Acontrolling the rate;- of: flow: of liquid from.. themotor andf aVV controller this purpose is illustrated in.- partirr. Figure. `3.. The difference between this and the controllerrillustrated inligure Zia-the pressure-.regulatingvalve andthe .arrangement for. operating thisfnvalve. Tllevalvetl is;replacedibytarvalveil;j .The over@ 'flowA valve 9, .the low pressure valve lHl; .the con.- .trolivalveV 12T-pilotn valvel3 and.. advancing: valve ilare the samein. this modified form ocontnoller aatheyare inftheorm shown in Figure- 2. The .only differences, Areside in1the valvef4$-l theeports cooperating .therewithy .the arrangemenizsforr se;- lectingrl between. two .pressuresy the.A pressure` :to action the. valve andi the provisions of' grooved extensions.. 21h. and 21d" on theportsA 21h and ltTlLpthe: purpose of.V which. will. hereinaiter api- PCEI Y 'The regulating.l valve4 43: is a` halancedvpiston .valvehaving a reduced central-portionaafand it is. mounted. in the. borel 2d. in. the,4 control block;

Cooperating:y with, the valve. thereare:` an.A exhaustV p ont 42:21 and. a high ,pressure port. 42e, the .425 andAZc being spaced apart longitudinally of tl'eborei Acting between the plate-2li."r covere ingthelowerendiof the bore 2d, andthe adjacent end" o. the valve;` there .istv aL springA Mrwhich a force. onf-the valve. equivalent total-pres"- sureyoi one. hundredpoundsper: square inch; thel'ow. pressurel oilsupply. might be. used. in place othisspring.V 'lheiorceA of the spring-LL tends tomovathe valve. to..cut on?, the. exhaust. port .42h andlmaintain thahigh pressure .portopem .Opposedtotheiorcefof thesprngl, there is thebackpressureof. themotor. and forV the pur.- pose. ot applying thisspressurefto .thervalve vthe selectiva valve. I5, is, provided;A4 .The valve 4i is `a valveand ,it is slidably mountedin .a

dlongitudinalvbor e -.46a in.'za..bloclv 4.6.. The block AB] hasi twn ports 45h `and 46clvwhich; are con.-

nected-.asshuwn to the motor. ports. end passages 21p, and. 21d.. ports. lb and..4'c1.aref.suaced apart longitudinally: ot.- thee valve;- and. include groovedi extensions: b5 and. Get whlclnextend longitudinally of; the'fvalve-A in; opposite-directions so that. theport lbfis never. cut-olli from-com: rnunicationv with ai chaxnber.-46d.v formed .between the plate 'M'7 andtheadjacentt end ofv the valve andrthe porti 46c-'is `never cut .oilifromcommuni'-^ cation .with .the'chamberz 46e formedbetweenfthe inner; end of the-bore 46a,- and the adjacent. end of. thefvalve'. Thevalve. l5 selectively controls communication `between the -portslband A Gc: and ar transverse passage: 461* which, through alongltudinal. groove.' 45g in.V the: surface: oi: the. block 46, communicates withachamber I1 formedbetweenzthe inner on lower. end-.ot the-block 4E and thev adjacent endet; the, valve 43.- projection 4-3d on the gendof.: the-valve; 43 limits. the move,- ment voi thefvalve inthe :direction ,of the hlocklli.

With; the above described'. arrangement, `the pressureof. the oilin-theaport 42o is regulated-by: the: difference ini the i force-v exertedxby the. spring; andthebackfpressureonzthefmotor; the valve 45.- selectsf the -oilf of lower. pressure in thev ports 4Gb and :46c tofbe delivered tothe passage 46j.. Inzthe position:in-whichthefvalve, I 2 is illustrated in Figure 3;oil; under' pressure: trickles. through the-extensionsflbf" and 21d" of the ports. 2lb and-21d. This-oil actszonv both sides ofv thefpiston valvev 'and the. Valvei remains intheA position in which it is illustrated in Figure 3.. 4lnthis position of,k the valve.I Mathe. motor. is, of course inoperative.v Let. us now aume thevalve. 12.13 moved upwardly, in-.themannerheretofore eirplained, so that it. istV oil lap-with:- respect tothe ports4 12711::` and. 21d.. Under; these. assumed conditiona, thev p ort ZTI-Irisconnected to. the high pressure.- port. 21cfand the/port 21d. is .connected tofthe` exhaust port 23e; Oil-funden high pressure thenentersthemotor. passage.' 2f and the. port 4Gb. Theftpressureimtheport 46c:is,.of course; reduced as vthis'- port'nis connected.` tothe lowr pressure; :side ofi themotor.' the:l motorA passage 2g.: Thee pressure acting in. the` chamber. Aid, therefore', predominates', .forcal the valve 45 down and :the port Mcis placed inlcnmmunication with thepassage Mit and chamber 4L Likewise, if; the valve: l2 is moved'downwardlwoi lapwithlrespect tarthe'ports 21h andi 2Jd,.'the; port Nhwillfbe placed into.-` communication. with7 the low` pressure side of .the motor andthe port- 2\1d.withthe high pressure; the: pressure in; the chamber. 46ev will then predominate and theportlhwillbc placed intor communication withl the: passageA (Gf. andfchamher VII'IL.

valvez lliisinovedloff lupi, thereoil flowing throughsthisevalve fromythe-flow pressure sidefof the motor to: the.' exhaust is-throttled` A certain' baci: pressure inthe motor. is, therefore, louiltv up in thepassage .communicatingl with the llow pres-v sure side of the motor. The value-ot thislbaclcpressure, is a function ,.ot. the. pressure o the. oil supply and it. may therefore. be, varied.. or as desiredl here., it, man bemaintained, constant. by controlling the pressureioiztheoilsupply.. In` the arrangement.- illustrated. im Eigure 3, this4 hack pressuremaintained constanti at one. hundred pounds per squareinch. Itthe back: prsureV exceeds.v this value inzthechamberxltl it willrmove; thevalve 4.3 against; theractionY of the spring` 44. to placethe; exhaust porty 2b. into communication.. with. the high pressure port 42e and. thu: effect a. reduction vin.theepressurc ot the oil.. suppliedl to-,the motor. As; a: mattenotfachduring, operatio thevalve.- 43.. is regulating the. extentor thecommunicationbetween. theportszllb and.

13 42e and the oil pressure in the passages communicating with the low pressure side of the motor is maintained at one hundred pounds per square inch irrespective of the load on the motor or the valve opening.

By thus controlling the back pressure on the motor or the pressure at the low pressure side of the motor, a constant pressure drop 'is maintained across the port of the valve controlling communication between the low pressure side of the motor and the exhaust. The rate of flow of oil through the valve is, therefore, proportional to the extent the valve is opened. Consequently, the rate of ow of oil through the motor and, therefore, the speed of the motor are proportional to the opening of the valve.

The velocity of the motor may also be controlled by adjusting the pressure of the supply in accordance with the difference in the pressure in the motor leads, that is, the drop in pressure across the motor. The pressure regulating valve and mechanism for actuating the valve illustrated in Figure 4 are adapted to regulate the pressure of the supply in this way. In Figure 4, the pressure regulating valve 48 is of the balanced piston valve type similar to the regulating Valve shown in the modilcation illustrated in Figure 2. The valve 48 may be, as it is illustrated, slidably mounted in the bore 2d of the control block 2 adjacent the plate 20. The valve coperates with longitudinally spaced, circumferential exhaust and pressure ports 43a and 43h respectively. Through the lower end of the valve there is a passage 48e which places a chamber 48d formed between the end of the valve and the plate 2l! in communication with the chamber formed by the reduced portion of the valve. Oil under pressure entering through the pressure port 48h enters the chamber 48d through the passage 48o and acts upon the end of the valve tending to move the valve upwardly from the position shown in Figure 4. As the valve moves upwardly from the position shown, the exhaust port is opened to the pressure supply and thus reduces the pressure of the oil in the pressure port 48o.

Movement of the valve under the action of the oil in the chamber 48d is resisted by the force exerted by the low pressure oil and the difference between the forces exerted by the pressure of the oil in the motor passages, in other words, a force that is proportional to the drop in pressure across the motor. The low pressure oil acts upon the upper end of the valve 48 in a cham ber 48e to which the low pressure oil is admitted through a port ff The chamber 48e is formed between the end of the valve 48 and the end of a block 4S which is secured in the bore 2d against movement therein by a set screw 59. Extending through and slidable in a longitudinal bore in the block 49, there is a rod 5| having a collar 52 formed thereon above the upper end oi the block 49. The section of the rod above the collar 52 extends through a longitudinal bore in a solid plunger 53 which normally abuts against the collar 52. Another plunger 54 is mounted in the bore 2d above the plunger 53. A set screw 55 extends into the bore 2d between the plungers 53 and 54 and forms a limit stop for the upward movement of the plunger 53. A pin 56 secured to the plate 2| forms a similar limit stop for upward movement of the plunger 54.' In the position in which the valve 48 is shown in Figure 4, that is, with the exhaust port Closed, the upper end of the rod 5| extends slightly beyond the limit stop 55, when the opposite end is abutting against the 'f ates to eiect this result as follows: If the valve l2 is actuated so that the port 21d is connected `area of the rod 5|):

valve 48. Three ports 48g, 58h and 48i communicate with the`bore 2d for the purpose of supplying oil for the actuation of the plungers 53 and 54. The port 48g communicates with the bore 2d above the plunger 54, the port 48h communicates with the bore 2d between the plungers 53 and 54, and the port 481' communicates with the bore 2d between the upper end of the block e9 and the lower end of the plunger 53. The ports 45g and 482' are connected together and to the motor port Zld of the valve sleeve 21, and the port 48h is connected to the motor port 2lb of the valve sleeve 21.

With the arrangement described above, the force exerted through the rod 5| and the valve 4S represents a force which is the diierence between the force exerted by the oil in the motor leads, and which is proportional to a force exerted by oil under va pressure equivalent to the drop in pressure across the motor. This/force is added to the force exerted by the low pressure oil so that the pressure of the oil supply to the motor may be represented by the Vfollowing equation (disregarding the slight diierence in areas of the ends of the plunger 53 due to the the pressures in the motor passages; and the L represents the pressure of the low pressure oil. The arrangement illustrated and described operto the oil supply and the port 2lb is connected to the exhaust, oil under pressure, that is, the pressure of the oil in the motor passage which communicates with the port 21d will be admitted to the port 481' between the upper end of the block 45 and the lower end of the plunger 53 and also to the port 48g above the plunger 54. The space between the plungers 53 and 54 will be connected to the low pressure side of the motor, i. e. the motor port 2lb. The plungerv 53 will thus be moved upwardly against the stop 55. The plunger 54 will be moved downwardly against the end of the rod 5|. This occurs because the pressure of the oil below theplunger 53 and above the plunger 54 is greater than the pressure of the oil between the plungers. The plunger 53 will .thus have no eiect upon the valve asV it will not exert any force upon the rod 5|. The plunger 54 will however exert a force upon the rod 5| which force will be proportional to the diierence between the pressure admitted between the plungers 53 and 54, that is, the pressure of the oil at the low pressure side of the motor and the pressure of the oil admitted above the plunger 54, that is, the pressure of the oil at the high pressure side of the motor. The force therefore exerted upon the rod 5| will be proportional to the drop in pressure across the motor and this force will, through the rod 5|, be added to the force exerted by the low pressure oil so that the pressure of the oil in the pressure port 48h will be one hundred pounds per square inch greater than the force exerted through the rod 5| Y If on the other hand, the valve S2 is so moved that the port 2lb and thejrnotor passagel communicating therewith is connected tothe high pressure oil and the port 21d and the motor pas,- sage connected therewith is connected to the exhaust, oil from the passage on the high presi 115 sure, side;v or the motor* will bez admittedv between theplungers: 53 and 5.42 and oil at the pressure of thefiow. pressureside. ofv themotor-Will be admitted aboveY andbelow the.- plungersy 53. and 54.. With this. condition existing, the; plunger '4 will. be moved' against its` limit stop 56, the, plunger 53 will bemoved against the collar. 52.011 the rod 5t and through this collar willi exert a force. upon the; valve 48. The force exerted by the oil between.- the plungers will, however, be resisted by the iorcev exerted by the oil below the plunger 53 which is the pressure of the oil on the low pressure side of the motor. 'Ihere is thus: exerted upon. they rod 5? a force which isfproportional. to thefpressure drop acrossfthemotor as represented by-the formula given above.V

- By thus controlling the.V pressurer of` the oil supplied to the motor in accordance with the pressure drop` across the motor, there is maintained a. constant pressure drop across the. valve controlling the supply of oil to the motor and the. passage of oil from the. motor to the-exhaust. Thisy arrangement givesamore delicate control of. thefvelooity offthe motor andas inthe embodiv mentssillustratedin Figures 2 and 3, the velocity of the motor will be proportional tozthe vmovement of the valve rod 13a.

It is obvious that various changes may be made by those skilled in the art in the details: of. the embodiments oi thein-ventonv illustrated in the drawings and. described` above within the principle and scope of. the.. invention as expressed inthe appended claims.

We claim:

1.. In a hydraulic power` system including a' hydraulic mediumunderr diilerentr and varying pressures, pressure control. meansfur-4 affecting the. system andoperating-means4 therefor: includ'- ingmeans for selectively applying to thefcontrol means the force exerted bythe portion. or the hydraulic medium under the highest pressure.

2. In ahydraulic. powersystem including several passages containing a hydraulic medium under differentand varying'pressures, pressure control means for affecting-the system and operating means therefor connected. to the severa-l passages, the operating means including-means for/selectively applyingv tothe control means the force exerted by the hydraulic supply thereto underV the highest pressure.

3. In a hydraulic, power' system including several passages containing a hydraulicvmedium underL diierent and varying pressures, a pres.

sure-regulating valve and means for effecting the; operation of the. valve including means for exerting a forceto actuate the valve in one direction, and means for exerting'a force on the valve in the opposite direction including means forselectively applying the force exerted by the highest of several' pressures to the valve, and connections between the several passages and saidl'ast mentioned' means.

4f. In a hydraulic powerv system' including several' passages containing aA hydraulic. medium under different and varying pressures, a pressure-regulating, valve..and means for effecting movement of the valve including a connection. between the valve andone o saidpassages. to apply the force, ofthe hydraulic. medium. to effect movement ofv the valve. in one. direction and means for exerting a force on. the.. valve in the.. opposite direction including means for selectively applying. the; torcevv exerted by the highest oi several pressures` to the valve. and.

126 connectionsbetween thefremaind'er ottheseveral passages and said last mentioned means'.

5. In; a hydraulic powersystem, a( source'sot liquid: of substantially constant displacement', a hydraulic motor connected. thereto and a controller intermediate the supply of. liquid under pressure andy the` motor; the controller includingafour-way controlvalve andmeans for maintaining aV constant pressure dropacross the valve comprisingy a pressureregulating valve Vfornregu lating; the pressure in advance of said` control valve and operating` means for the pressure regulating,Y valve; including means acting upon the-valve to open the valve in accordance with the pressure on the supplyv sideV of the control valve, and means opposing the opening of the valve in accordance. with the; sumV of; a constant pressure and; thefhighest of the tvvoV pressuresy at the motor.

6. A. controller for. a lrvdrauiic motor comprising a four-way control. valve and means' for maintaining a constant pressureacross the control valve. including a. pressure regulating valve', aV connection for connecting the supply end` of thecontrolv valve to -move the pressure regulating.I valve in one direction, means' for. exerting a constant. force onV the valve to move theivalvefin the opposite, direction; and means for. selec.- tively adding* to the` constant force thev force exerted by the.; hydraulic medium of highest pressure at the motor.;

7.111: a` hydraulic. power system,V a source ot liquid of. substantially constant displacement, a controller` connected thereto for controlling the-now of liquid. and' including passages' containing hydraulic: medium; under different and varyingpressures, a control valve.v within the controller, connections for' applying: the pressure of'v the supply' of liquid in a'. direction to open the valve, means for applying. ar` constant pressure to effect'. the operation of the valve in the opposite direction, and means for selecting the pressure of the hydraulic-medium in one of the several passages. in accordanceV with. the relative values of the-pressurestin the passages and adding the force-thereof to the constant forceacting on the. valve.

8. In a hydraulic power system, a source of liquid ofsubstantially constant displacement, a hydraulic motor' connected thereto andl a controller-for controlling the hydraulic motor including a. pressure-actuated. control' valve intermediatethe source ofliquid and the motor, connections for applying the pressure of the source ofliquidrtozeiectthe opening of' the control valve, means for. applying'av constant pressure to effect operationy of theivalve inthe opposite direction and means for selecting the pressure of the hydraulic medium in oneofY the motor leads in accordance with the relative values of the pressures inthe motor leads and adding the selected pressure to thezconstant pressure. acting on the control valve..

9i In a hydraulic' power system, a source of liquid of substantially constant displacement, a hydraulic motor connected thereto and a controller for controllingV the hydraulic motor including a throttle valve@ a pressure-actuated control. valve intermediate` the sourcer of' liquid and. the: motor, connections for applying the pressureA of, the:A sources ott liquid to eiTectf the opening of thecontrollvalvef, means for'applyi'ng aV constant: pressureJtcz. eilect operation ot the valve in the. opposite-v. direction and' means for selecting' the?` pressure ci' the hydraulic medium l? in one of the vmotor leads in accordance with the relative v alues of the pressures in the motor leads and adding the selected pressure to the constant pressure acting on the control valve.

10. In a hydraulic power system including several passages containing therein hydraulic medium under different and varying pressures, means operative to vary the iiow of hydraulic medium in certain of said passages including means for varying the cross-sectional area of the said certain passages and for changing the direction of ow of the hydraulic medium therein, and means for regulating the pressure drop across the variable cross-sectional area of one of said certain passages.

11. In a hydraulic power system including several passages containing therein hydraulic medium under different and varying pressures, means operative to vary the flow of hydraulic medium in certain or said passages including means for varying the cross-sectional area of the said certain passages and for changing the direction of flow of the hydraulic medium therein, and means for maintaining the ilow of hydraulic medium through one of said regulated passages constant for any given cross-sectional area thereof.

12. In a hydraulic power system including several passages containing therein hydraulic medium under dierent and varying pressures, means operative to Vary the flow of hydraulic medium in certain of said passages including means for varying the cross-sectional area of the said certain passages and means for changing the direction of iiow of the hydraulic medium therein, and means for maintaining the pressure drop across the variable cross-sectional area of one of said passages constant.

13. In a hydraulic power system including several passages containing therein hydraulic medium under different and varying pressures, means operative to vary the ilow of hydraulic medium in certain of said passages including means for varying the cross-sectional area of the said certain passages and for changing the direction of flow of the hydraulic medium therein, and means for maintaining thev flow of hydraulic medium through one of said regulated passages constant for any given cross-sectional area thereof including a pressure regulating valve, and means for selectively applying thereto a force in accordance with the relative value of the pressure of the hydraulic medium in certain of said passages.

14. In a hydraulic power system including several passages containing therein hydraulic medium under different and varying pressures, means operative to vary the flow of hydraulic medium in certain of said passages including means for varying the cross-sectional area of the said certain passages and for changing the direction of i'low of the hydraulic medium therein, and means for maintaining the flow of hydraulic medium through one of said regulated passages constant for any given cross-sectional area thereof including a pressure regulating valve, means for applying a force of constant magnitude thereto, and for selectively applying to the valve in addition to said force of constant magnitude a force in accordance with the relative value of the pressures of the hydraulic medium in certain of said passages.

15. In a hydraulic power system including several passages containing therein hydraulic medium under different and varying pressures, means operative to vary the ow of hydraulic medium 18 in certain of said passages including means for varying the cross-sectional area of the said certain passages and for changing the direction of flow of the hydraulic medium therein, and means for maintaining the flow of `hydraulic medium through one of said regulated passages constant for any given cross-sectional area thereof including a pressure regulating valve, connections for applying the pressure of the hydraulic medium in one of said passages to move the valve in one direction, means for applying a force of constant magnitude to effect moving of the valve in the opposite direction, and means for selectively adding to said force of constant magnitude, a force in accordance with the relative value of the pressures of the hydraulic medium in certain of said passages.

16. In a hydraulic power system including several passages containing therein hydraulic medium under diiferent and variable pressures, means operative to vary the iiow of hydraulic medium in certain of said passages including means for varying the cross-sectional area of said certain passages and for changing the direction of flow of the hydraulic medium therein, and means for maintaining the low of hydraulic medium through one of said regulated passages constant for any given cross-sectional area thereof including a pressure regulating valve, connections for applying the pressure of the hydraulic mediin one of said passages to move the valve in one direction, means for applying a force of constant magnitude to move the valve in the opposite direction, and means for selectively adding to said force of constant magnitude, a force in accordance with the greater pressure of the pressures in two of said passages.

17. In a hydraulic power system, a source of hydraulic medium under pressure, a hydraulic motor connected thereto, and a controller for controlling the hydraulic motor including a control valve for controlling the cross-sectional area of the opening of the passage to the motor and the direction of iiow or the hydraulic medium, a pressure regulating valve for maintaining the fiow of hydraulic medium to the motor constant for any opening of said control valve, and means for actuating said pressure regulating valve including a connection for applying the pressure of the hydraulic medium supplied to the motor to move the valve in one direction, means Vfor applying a force of constant magnitude to move the valve in the opposite direction and means for selectively adding to said force of constant magnitude a force in accordance with the relative values of the pressures of the hydraulic medium in the motor leads.

18. In a hydraulic power system, a source of hydraulic medium under pressure, a hydraulic motor connected thereto, and a controller for controlling the hydraulic motor including a control valve for controlling the cross-sectional area of the opening of the passage to the motor and the direction of ow of the hydraulic medium, a pressure regulating valve for maintaining the iiow of hydraulic medium to the motor constant for any opening of said control valve, and means for actuating said pressure regulating valve including a connection for applying the pressure of the hydraulic medium Supplied to the motor to move the valve in one direction, means for applying a force of constant magnitude to move the valve in the opposite direction and means for selectively adding to said force of constant magnitude a force in accordance with the higher 19 of the pressures of the hydraulic medium in the motor leads.

19. In a hydraulic powersystem, a source of hydraulic medium under pressure, a hydraulic motor connected thereto, and a controllerl for controlling the hydraulic motor intermediate the source of hydraulic medium and the motor, the controller comprising a four-Way control valve for controlling the cross-sectional area of the passages leading to the motor and the direction of ow of hydraulic medium through the passages, a pressure regulating valve for maintaining the pressure drop across the four-Way Valve constant, and means for actuating the four-way valve including a connection for applying the pressure of the hydraulic medium delivered to the four-way valve to the pressure regulating valve to effect movement thereof in one direction, means for applying a force of constant magnitude to effect movement of the pressure regulating valve in the opposite direction, and means for selectively adding to the force of constant magnitude a force in accordance with the relative values of the pressuresof the hydraulic medium in the motor leads.

20. In a hydraulic power system, a source of hydraulic medium under pressure, a hydraulic motor connected thereto, and a controller for controlling the hydraulic motor intermediate the source of hydraulic medium and the motor, the controller comprising a four-Way control valve for controlling the cross-sectional area of the passages leading to the motor and the direction of ow of hydraulic medium through .the passages, a pressure regulating valve for maintaining the pressure drop acrossthe four-Way valve constant, and means for actuating the four-Way valve including a, connection for applying the pressure of the hydraulic medium delivered to the four-way valve to the pressure regulating valve to eiect movement thereof in one direction, means for applying a force of constant magnitude to effect movement of the pressure regulating valve in the opposite direction, and means for selectively adding to the force of constant magnitude a force in accordance with the higher of the pressures of the hydraulic medium in the motor leads. a

21. A controller for a hydraulic motor comprising a control valve for controllingthe crosssectional area of the openings of passages to the motor and the direction of ow of hydraulic me- 20 dium in said'passagesto the motor, and a pressure regulating' valve for regulating the'pressure of the hydraulic medium on the supply side of said control valve, and' means for operating said pressure regulating'valve including a connection for applying the pressure of the hydraulic medium on the supply side of said control valve to one end of the pressure'regulating valve, means for applyinga force of constant magnitude to the other end of the valve and means for selectively adding to the force of constant magnitude a force in accordance with the relative values of the pressure of the hydraulic medium in the passages connected to the motor.

22. A controller for a hydraulic motor comprising a control valve for controlling the crosssectional area lof the openings of passages to the motor and the direction of ow of hydraulic medium in said passages to the motor, and a pressure regulating valve for regulating the pressure of the hydraulic medium on the supply side of said control valve, and means for operating said pressure regulating valve including a connection for applying the pressure of the hydraulic medium on the supply side of said control valve to one end ofthe pressure regulating valve, means for applying a force of constant magnitude to the other end ofthe valve and means for selectively adding to the force of constant magnitude a force in accordance with the higher of the pressures of the hydraulic medium in the passages connected to the motor.

EDWARD J. POITRAS. JAMES D. TEAR..

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,939,113 Ferris Dec. 12, 1933 2,004,522 Douglas June 11, 1935 1,972,462 Schafer Sept. 4, 1934 2,005,732 Ernst etal June 25, 1935 2,005,731 Ernst June 25, 1935 2,006,311 Ernst June 25, 1935 2,028,766 Ernst Jan. 28, 1936 1,964,196 Cuttat June 26, 1934 1,467,522 Amsler Sept. 11, 1923 1,964,398 Ferris June 26, 1934 2,111,964 Crane Mar. 22, 1938 

